1. Field of the Invention
Such overflow or transfer recesses, the position of which is determined by the leading piston corner in a working chamber created in the dead center position, have the purpose to relieve the gas pressure, which still exists in the chamber created in the dead center position after closing the discharge or outlet, to the leading or preceding chamber which is created at the beginning of the compression cycle, and thus to avoid the negative torque otherwise caused by this remaining pressure during further rotation of the piston beyond its dead center position.
2. Description of the Prior Art
The overflow recesses can, as shown in German Offenlegungsschrift No. 21 57 546, be radial channels deepened into the surface path or runway and extending in direction of rotation of the piston, between which channels the surface of the mantle path or runway remains as webs or at the edge of which the same remains as side strips in order to prevent the radial sealing strips from dropping into these channels. It has been found, however, that in operation the path or runway surface of these webs and side strips can be destroyed in a short time by beating-in of the sealing strips.
The reasons for the foregoing can be found in a canting or tilting of the radial sealing strips, which as a consequence of elimination of the pressure in the following chamber during approaching of the overflow recess are tilted by recess gas pressure existing again, and by the friction of the radial sealing strips against the surface raceway or path; this traps the recess gas in the recess, and prevents the release or relieving thereof. The strip is therefore beaten by the groove gas, accompanied by a hammering noise, against the webs and edge strips of the surface runway or path. The braking effect thereby exerted upon the piston additionally leads to a beating of the gearing. The beating or striking of the tilted and consequently jammed strip leads to the noted wear of the surface runway in the region of the overflow recesses; this wear can amount to one half to one millimeter in 10 to 20 hours, and can lead to rapid unserviceability of the machine. Tests of 100-hour duration could not be completed with such compressors.
Such an effect cannot occur in the side parts of the housing with an axial arrangement of the overflow recesses or grooves as illustrated in German Offenlegungsschrift No. 27 00 731, corresponding to U.S. Pat. No. 4,150,926--Eiermann dated Apr. 24, 1979, since the recess gas can escape laterally toward the overflow recesses. A disadvantageous effect, however, with this arrangement is that, as seen in the axial direction, the piston flank approaching the overflow recesses is at a very acute angle with respect to the surface runway or path. Only a very small cross section is available for the transfer of the gas into the preceding chamber upon entry into the lateral overflow recesses. The desired relief or pressure release of the residue pressure in the chamber which traverses or passes over the dead center position therefore does not occur quickly enough to effect a smooth or quiet running of the compressor, and to effect the greatest possible saving of power. Although this cross sectional constriction or narrowing-down would not be disadvantageous with the first mentioned radial arrangement of the overflow recesses, the described wear of the surface runway or path, and the unacceptable non-quiet running and greater consumption of power caused thereby, mandates axial arrangement of the overflow recesses.
It is an object of the present invention to improve the flow rate through the axial overflow recesses.